-- Copyright (c) 2020 rxi
-- this software and associated documentation files (the "Software"), to deal in
-- the Software without restriction, including without limitation the rights to
-- use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
-- of the Software, and to permit persons to whom the Software is furnished to do
-- so, subject to the following conditions:
--
-- The above copyright notice and this permission notice shall be included in all
-- copies or substantial portions of the Software.
--
-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-- OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-- SOFTWARE.
--

-- this software and associated documentation files (the "Software"), to deal in
-- the Software without restriction, including without limitation the rights to
-- use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
-- of the Software, and to permit persons to whom the Software is furnished to do
-- so, subject to the following conditions:
--
-- The above copyright notice and this permission notice shall be included in all
-- copies or substantial portions of the Software.
--
-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-- OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-- SOFTWARE.
--
local EM,FB=...
local json = { _version = "0.1.2" }
-------------------------------------------------------------------------------
-- Encode
-------------------------------------------------------------------------------
local encode
local escape_char_map = {
  [ "\\" ] = "\\\\",[ "\"" ] = "\\\"",[ "\b" ] = "\\b",[ "\f" ] = "\\f",[ "\n" ] = "\\n",[ "\r" ] = "\\r",[ "\t" ] = "\\t",
}

local escape_char_map_inv = { [ "\\/" ] = "/" }
for k, v in pairs(escape_char_map) do escape_char_map_inv[v] = k end
local function escape_char(c) return escape_char_map[c] or string.format("\\u%04x", c:byte()) end
local function encode_nil(_) return "null" end


local function encode_table(val, stack)
  local res = {}
  stack = stack or {}
  -- Circular reference?
  if stack[val] then error("circular reference") end
  stack[val] = true
  if rawget(val, 1) ~= nil or next(val) == nil then
    -- Treat as array -- check keys are valid and it is not sparse
    local n = 0
    for k in pairs(val) do 
      if type(k) ~= "number" then error("invalid table: mixed or invalid key types") end
      n = n + 1
    end
    if n ~= #val then error("invalid table: sparse array") end
    -- Encode
    for _, v in ipairs(val) do table.insert(res, encode(v, stack)) end
    stack[val] = nil
    return "[" .. table.concat(res, ",") .. "]"
  else
    -- Treat as an object
    for k, v in pairs(val) do
      if type(k) ~= "string" then error("invalid table: mixed or invalid key types") end
      table.insert(res, encode(k, stack) .. ":" .. encode(v, stack))
    end
    stack[val] = nil
    return "{" .. table.concat(res, ",") .. "}"
  end
end

local function encode_string(val) return '"' .. val:gsub('[%z\1-\31\\"]', escape_char) .. '"' end

local function encode_number(val)
  -- Check for NaN, -inf and inf
  if val ~= val or val <= -math.huge or val >= math.huge then error("unexpected number value '" .. tostring(val) .. "'") end
  return string.format("%.14g", val)
end

local type_func_map = {
  ["nil"] = encode_nil, ["table"] = encode_table,["string" ] = encode_string,["number"] = encode_number,["boolean"] = tostring,
  --   [ "function" ] = tostring,
}

encode = function(val, stack)
  local t = type(val)
  local f = type_func_map[t]
  if f then return f(val, stack) end
  error("unexpected type '" .. t .. "'")
end

function json.encode(val,...)
  local extras = {...}
  if #extras>0 then error("Too many arguments to json.encode?",2) end
  local res = {pcall(encode,val)}
  if res[1] then return select(2,table.unpack(res))
  else 
    local info = debug.getinfo(2)
    error(string.format("json.encode, %s, called from %s line:%s",res[2],info.short_src,info.currentline))
  end
end
-------------------------------------------------------------------------------
-- Decode
-------------------------------------------------------------------------------
local parse
local function create_set(...)
  local res = {}
  for i = 1, select("#", ...) do res[ select(i, ...) ] = true end
  return res
end

local space_chars   = create_set(" ", "\t", "\r", "\n")
local delim_chars   = create_set(" ", "\t", "\r", "\n", "]", "}", ",")
local escape_chars  = create_set("\\", "/", '"', "b", "f", "n", "r", "t", "u")
local literals      = create_set("true", "false", "null")

local literal_map = { [ "true"  ] = true, [ "false" ] = false, [ "null"  ] = nil, }

local function next_char(str, idx, set, negate)
  for i = idx, #str do if set[str:sub(i, i)] ~= negate then return i end end
  return #str + 1
end

local function decode_error(str, idx, msg)
  local line_count = 1
  local col_count = 1
  for i = 1, idx - 1 do
    col_count = col_count + 1
    if str:sub(i, i) == "\n" then line_count = line_count + 1 col_count = 1 end
  end
  error( string.format("%s at line %d col %d", msg, line_count, col_count) )
end

local function codepoint_to_utf8(n)
  -- http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=iws-appendixa
  local f = math.floor
  if n <= 0x7f then return string.char(n)
  elseif n <= 0x7ff then return string.char(f(n / 64) + 192, n % 64 + 128)
  elseif n <= 0xffff then return string.char(f(n / 4096) + 224, f(n % 4096 / 64) + 128, n % 64 + 128)
  elseif n <= 0x10ffff then return string.char(f(n / 262144) + 240, f(n % 262144 / 4096) + 128, f(n % 4096 / 64) + 128, n % 64 + 128) end
  error( string.format("invalid unicode codepoint '%x'", n) )
end

local function parse_unicode_escape(s)
  local n1 = tonumber( s:sub(3, 6),  16 )
  local n2 = tonumber( s:sub(9, 12), 16 )
  -- Surrogate pair?
  if n2 then return codepoint_to_utf8((n1 - 0xd800) * 0x400 + (n2 - 0xdc00) + 0x10000)
  else return codepoint_to_utf8(n1) end
end

local function parse_string(str, i)
  local has_unicode_escape = false
  local has_surrogate_escape = false
  local has_escape = false
  local last
  for j = i + 1, #str do
    local x = str:byte(j)
    if x < 32 then decode_error(str, j, "control character in string") end
    if last == 92 then -- "\\" (escape char)
      if x == 117 then -- "u" (unicode escape sequence)
        local hex = str:sub(j + 1, j + 5)
        if not hex:find("%x%x%x%x") then decode_error(str, j, "invalid unicode escape in string") end
        if hex:find("^[dD][89aAbB]") then has_surrogate_escape = true
        else has_unicode_escape = true end
      else
        local c = string.char(x)
        if not escape_chars[c] then decode_error(str, j, "invalid escape char '" .. c .. "' in string") end
        has_escape = true
      end
      last = nil
    elseif x == 34 then -- '"' (end of string)
      local s = str:sub(i + 1, j - 1)
      if has_surrogate_escape then s = s:gsub("\\u[dD][89aAbB]..\\u....", parse_unicode_escape) end
      if has_unicode_escape then s = s:gsub("\\u....", parse_unicode_escape) end
      if has_escape then s = s:gsub("\\.", escape_char_map_inv) end
      return s, j + 1
    else last = x end
  end
  decode_error(str, i, "expected closing quote for string")
end

local function parse_number(str, i)
  local x = next_char(str, i, delim_chars)
  local s = str:sub(i, x - 1)
  local n = tonumber(s)
  if not n then decode_error(str, i, "invalid number '" .. s .. "'") end
  return n, x
end

local function parse_literal(str, i)
  local x = next_char(str, i, delim_chars)
  local word = str:sub(i, x - 1)
  if not literals[word] then decode_error(str, i, "invalid literal '" .. word .. "'") end
  return literal_map[word], x
end

local function parse_array(str, i)
  local res = {}
  local n = 1
  i = i + 1
  while 1 do
    local x
    i = next_char(str, i, space_chars, true)
    -- Empty / end of array?
    if str:sub(i, i) == "]" then i = i + 1 break end
    -- Read token
    x, i = parse(str, i)
    res[n] = x
    n = n + 1
    -- Next token
    i = next_char(str, i, space_chars, true)
    local chr = str:sub(i, i)
    i = i + 1
    if chr == "]" then break end
    if chr ~= "," then decode_error(str, i, "expected ']' or ','") end
  end
  return res, i
end

local function parse_object(str, i)
  local res = {}
  i = i + 1
  while 1 do
    local key, val
    i = next_char(str, i, space_chars, true)
    -- Empty / end of object?
    if str:sub(i, i) == "}" then i = i + 1 break end
    -- Read key
    if str:sub(i, i) ~= '"' then decode_error(str, i, "expected string for key") end
    key, i = parse(str, i)
    -- Read ':' delimiter
    i = next_char(str, i, space_chars, true)
    if str:sub(i, i) ~= ":" then decode_error(str, i, "expected ':' after key") end
    i = next_char(str, i + 1, space_chars, true)
    -- Read value
    val, i = parse(str, i)
    -- Set
    res[key] = val
    -- Next token
    i = next_char(str, i, space_chars, true)
    local chr = str:sub(i, i)
    i = i + 1
    if chr == "}" then break end
    if chr ~= "," then decode_error(str, i, "expected '}' or ','") end
  end
  return res, i
end

local char_func_map = {
  [ '"' ] = parse_string, [ "0" ] = parse_number, [ "1" ] = parse_number,[ "2" ] = parse_number,
  [ "3" ] = parse_number, [ "4" ] = parse_number,[ "5" ] = parse_number,[ "6" ] = parse_number, [ "7" ] = parse_number,
  [ "8" ] = parse_number, [ "9" ] = parse_number, [ "-" ] = parse_number, [ "t" ] = parse_literal,
  [ "f" ] = parse_literal, [ "n" ] = parse_literal, [ "[" ] = parse_array,[ "{" ] = parse_object,
}

parse = function(str, idx)
  local chr = str:sub(idx, idx)
  local f = char_func_map[chr]
  if f then return f(str, idx) end
  decode_error(str, idx, "unexpected character '" .. chr .. "'")
end

function json.decode(str)
  local res = {pcall(function()
        if type(str) ~= "string" then error("expected argument of type string, got " .. type(str)) end
        local res, idx = parse(str, next_char(str, 1, space_chars, true))
        idx = next_char(str, idx, space_chars, true)
        if idx <= #str then decode_error(str, idx, "trailing garbage") end
        return res
      end)}
  if res[1] then return select(2,table.unpack(res))
  else 
    local info = debug.getinfo(2)
    error(string.format("json.encode, %s, called from %s line:%s",res[2],info.short_src,info.currentline))
  end
end

FB.json = json